Pulverized fuels are understood to include finely-ground coals of different degrees of carbonization, dusts made of biomasses, products of the thermal pretreatment such as coke, dried products by way of “torrefaction”, and fractions having high calorific value from municipal and industrial residual materials and waste materials. The pulverized fuels can be supplied as a gas-solid suspension or as a liquid-solid suspension to the gasification. The gasification reactors can be provided with a cooling screen or with a refractory lining, as disclosed in the patents DE 4446803 and EP 0677567. According to various systems introduced into technology, the crude gas and the molten liquid slag can be discharged separately or jointly in this case from the reaction chamber of the gasification device, as described in DE 19718131. A comprehensive description of the overall technology is found in J. Carl, P. Fritz, NOELL-KONVERSATIONSVERFAHREN, EF-Verlag, 1996, pages 25-53. Entrained flow gasification causes, as a result of the fuel particles, which are ground as fine as dust, and shorter reaction times in the gasification chamber, an increased dust fraction in the crude gas. This flue dust consists, in dependence on the reactivity of the fuel, of carbon black, unreacted fuel particles, and fine particles of slag and ash. The size varies between coarse particles having a diameter greater than 0.5 mm and fine particles having a diameter up to 0.1 μm. The separability of the particles from the crude gas is dependent on this diameter, but also on the composition thereof. Fundamentally, a differentiation can be made between carbon black and ash, on the one hand, and slag particles, on the other hand, wherein carbon black particles are generally smaller and more difficult to separate from the crude gas. Slag particles have a higher density and therefore a better separability, but in contrast thereto have a higher hardness and therefore an erosive effect. This results in increased wear in the classifying separators and lines which conduct crude gas, which can cause safety-relevant leaks and service life restrictions.
The previous prior art is documented in the patent DE 10 2005 041 930 and also in “Die Veredelung von Kohle [The Refinement of Coals]”, DGMK, Hamburg, December 2008, chapter “GSP-Verfahren [GSP Method]” pages 537-553, particularly in FIGS. 4.4.2.4.13 and 4.4.2.9.1. Accordingly, the gasification crude gas leaves the gasification chamber jointly with the slag formed from the fuel ash at temperatures of 1300-1900° C. and is cooled in a downstream quenching chamber by injection of excess water and freed of the slag and, to a small extent, of entrained dust. The further dust removal is performed in two Venturi washers connected in series, wherein the second washer has an adjustable throat to be able to keep the velocity in the throat constant even in the event of changing crude gas quantity and therefore to ensure a uniform velocity for the entrained dust. The gas purification was conceived for dust quantities up to 2 g/m3 under normal conditions and is intended to achieve a dust quantity of 1-3 mg/m3 under normal conditions at the outlet, which is necessary for disturbance-free operation of the downstream plants, such as CO conversion, synthesis, or gas turbines. To remove fine dusts, particularly of salt spray, a partial condenser is operated, in which the crude gas is cooled by 1-15° C., wherein the condensed water precipitates on the salt particles in particular and is removed from the crude gas stream by separation of the water droplets. For dust quantities greater than 2 g/m3 under normal conditions, this arrangement consisting of two Venturi washers and a partial condensation step is only partially adequate or is inadequate and can result in substantially higher dust concentrations in the intake of the CO conversion and also increased erosion in the Venturi washers and furthermore in soiling and blocking in the partial condenser and the downstream systems.